1. Field of the Invention
The present invention relates to nebulisers, normally used for administering a medicament to a patient by inspiration, the medicament being atomised into very small droplets or particles. Such a nebuliser comprises a gas exit, an outlet adjacent to the gas exit, and a deflector for deflecting a stream of gas issuing from the gas exit over the outlet for drawing a substance to be atomised from it, and for atomising the substance in the gas.
2. Brief Description of the Prior Art
In our earlier patent application EP 95307936.5 (publication number 0711609) we disclosed an atomiser of this kind in which atomisation only takes place during inspiration. This was achieved by the use of a movable deflector. The general principle of operation is shown in FIG. 1, in which gas issues from a gas exit 1 under pressure. An outlet 2 is disposed adjacent the gas exit. The outlet 2 includes a passageway 2a through which the substance to be atomised is led to an annular reservoir 2b which surrounds the gas exit 1. During inspiration, a deflector 3 is located above and in the path of the stream of gas issuing from the gas outline 1. This is shown in FIG. 1A, from which it will be seen that the gas is deflected above the outlet 2. This causes a low pressure region just above the outlet 2 which draws the substance to be atomised up through the passage 2a into the reservoir 2b, and causes the substance within the reservoir 2b to be atomised into the deflected gas stream. The atomised substance is carried away to be inhaled by the patient. As the patient stops inhaling, the deflector 3 swings about its pivot 3a and out of the path of the gas stream (FIG. 1C). The pressurised gas is then not deflected, but is directed straight upwards. No atomisation occurs because the stream of gas is not deflected across the outlet 2, and does not create a low pressure region just above the outlet by which medicament is drawn through the passage 2a.
This atomiser has been found to be extremely effective in using medicament much more efficiently, since atomisation only occurs during inspiration. However, it has been found that, as the deflector 3 moves out of the stream of gas, the liquid that is running along the edge of the deflector is sprayed into the top of the neubliser where it collects, much of it being unable to return to the reservoir, mainly due to the fact that the velocity of the gas emerging from the gas exit is extremely high, in the region of 500 m/sec. Any droplets that are carried up into the neubliser top will tend to shatter, and be further dispersed upon impact with the top. The high velocity gas stream hinders the return of the substance. This is shown in FIG. 1B.
This problem is also experienced by other arrangements, for example, the device shown in WO 97/29799 has the same problem. In this prior art, the outlet 2 is also adjacent to the gas exit 1, and a deflector 3 is used to deflect the stream of gas issuing from the gas exit 1, as shown in FIG. 2. During inspiration, the deflector 3 is located in the position shown in FIG. 2C. The deflector 3 directs the stream of pressurised gas across the outlet 2 causing atomisation. Once inspiration has ceased, the deflector 3 is raised into the upper part of the housing as shown in FIG. 2A. As the deflector is raised, more of the stream of gas passes up the air inlet duct carrying atomised medicament with it, as shown in FIG. 2B, until the device reaches the "off" position of FIG. 2A. The vertical stream of gas causes any liquid in the top of the nebuliser to be held there, rather than to drain back down into the base for re-atomisation.